In designing suspension systems for wheeled vehicles, and in particular trailers, engineers must consider the ride quality as well as the roll stiffness or stability desired for the trailer application. This consideration is even more challenging when evaluating the ride dynamics of the trailer so it will not appreciably degrade the mobility characteristics of its companion prime mover or pulling vehicle. Ride quality, of course, relates to the degree of hardness or softness of ride afforded by the spring and damping behavior of the suspension system. Roll stiffness refers to the resistance of the suspension system to rolling or tilting of the vehicle framework as might occur due to centrifugal force during a turning maneuver.
Prior art suspension systems attempting to seek these handling characteristics have incorporated various combinations of torsion bars, shock absorbing and dampening devices and stiffening tubes or sleeves. One example of a wheel suspension is shown in U.S. Pat. No. 2,465,098 issued Mar. 23, 1949 to Inskeep. In this trailer arrangement, the springing of the wheels results from the resiliency of the one piece axle or torsion bar which transmits all of the torsional load to a non-rotative, flattened position of the torsion bar connected to the center of the frame. Bearing sleeves are operative to prevent radial deflection of the torsion bar. A further showing of a suspension system having a sway torsion bar protected by a tube or sleeve is seen in U.S. Pat. No. 4,842,298 issued Jun. 27, 1989 to Jarvis.
Other examples of suspension systems utilizing shock absorbers interconnected with torsion bars are disclosed in U.S. Pat. No. 3,448,995 issued Jun. 10, 1969 to Stallard, et. al. and U.S. Pat. No. 4,337,958 issued Jul. 6, 1982 to Witt, et. al. In the '995 anti-roll system, a combined shock absorber and spring is mounted in proximity to each wheel on a trailer and joined to a single torsion bar which transfers moments from one wheel to the other wheel to reduce sway. In the '958 stabilization system for a snowmobile, a shock absorber is coupled to the center and restricts rotation of a torsion bar in response to a twisting force created at the steerable skis secured to the ends of the torsion bar. U.S. Pat. No. 4,641,856 issued Feb. 10, 1987 to Reichenbach further discloses an anti-roll stabilizer system employing separate shock absorbers operatively connected to the wheels and an adjustable hydraulic cylinder to selectively restrain the rotation of a torsion bar relative to a chassis to vary the roll stiffness of the suspension system.
Each of the above arrangements fails to define a suspension system wherein a twisting moment or torque transmitted to a torsion bar is efficiently absorbed in shared distribution between the frame and another portion of the torsion bar. In addition, these prior art suspensions cannot properly handle a bending moment or vertical deflection imposed on a wheel assembly. This is true, in part, either because of the absence of a stiffening sleeve or the simple inclusion of a sleeve about a torsion bar without providing proper support to prevent interference contact between the sleeve and torsion bar. Furthermore, none of these arrangements contemplates the reduction of wheel camber by proper bearing support of the stiffening sleeve. Moreover, predecessor designs also cannot provide shock absorbing and dampening devices in combination with torsion bar assemblies wherein the spring rate of the suspension system may be varied along with disposition of the framework by variably pressurizing the shock absorbing and dampening device.